1. Field of the Invention
The present invention relates to a type character selecting mechanism for a printing head to be used with a portable label printing and applying machine which is often referred to as a hand labeler or tagging machine.
2. Description of the Prior Art
In printing heads mounted in hand labelers or tagging machines, generally, a plurality of type bands or type rings bearing type characters on their outer surfaces are juxtaposed on a common axis. A desired band or ring is selected therefrom by means of a selecting knob or the like and is turned to select a desired type character for printing.
Recently, the so-called "POS" (i.e., Point of Sales System) has been developed, using a printing head for bar codes to be optically read. The bar codes are composed of symbol marks, each of which has several characters each indicating numerals from 0 to 9. But their specific structures and configurations have not yet been standardized and include a variety of systems for various codes. Some of such codes have been referred to as UPC, WPC and JAN.
However, most patterns are shared among these code systems. These patterns however permit selected inner characters to be interchangeable in order to provide information including a manufacturer or source code or a commodity code. Selected outer characters are either fixed since they are not expected to be changed or are, in effect, semi-fixed since they are seldom expected to be changed. The latter include guard codes, start codes, end codes or check codes.
In the bar code printing head according to the prior art, the type character selecting mechanism for the afore-mentioned semi-fixed characters has a construction identical to that of the type character selecting mechanism for the afore-mentioned changeable characters. A selecting knob is moved to slide in its axial direction to select one of the semi-fixed character bands or rings and the selecting knob is then turned to select the desired one of the characters. As a result, since the type selecting operations for both the changeable and semi-fixed types are common, an operator is liable to erroneously change the semi-fixed type characters, even when such change is not necessary, so that an erroneous print frequently results.